Controlled oxygen addition for metal material

ABSTRACT

Methods to form metal oxide material are described. In one process, an oxide film on a metal material is diffused throughout the metal material to form a preferred uniform metal oxide material. The present invention further relates to products formed by the process. Also, the present invention relates to the use of the products in capacitor anodes and other applications.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to metal, and more particularlyrelates to metal containing desired amounts of oxygen, such as metaloxide materials.

[0002] It has been found that oxygen enriched metal substrates offersome advantages over their pure metal counterparts. For example,capacitors made from oxygen enriched Nb have low leakage current and areless sensitive to contaminates such as carbon. It is proposed that thepresence of oxygen reduces the contamination level via oxidation duringthe high temperature manufacturing process. Though air or controlledatmosphere exposure can introduce oxygen into a metal substrate, precisecontrol of the process is far from simple. This results from the factthat many metal substrates, especially those in a high surface areapowdery form are highly reactive and the oxidation tends to belocalized, which makes controlled oxidation difficult.

[0003] Furthermore, the benefits of valve metal suboxides, such asniobium suboxides, in such applications as capacitor anodes has beenshown to be useful. In a typical process, niobium metal powder, forinstance, is mixed with niobium pentoxide and heat treated to form adesired niobium suboxide such as NbO. In the product made by thismethod, the physical structure of the raw materials typically remains.The residual niobium pentoxide structure, which can have a finemicrostructure, may inhibit to some extent the impregnation steps informing the finished capacitor. While the current method of formingvalve metal suboxides is very beneficial and provides many advantagesover standard capacitor anodes, methods to better improve the overallpentoxide and its use in an anode would be beneficial.

SUMMARY OF THE PRESENT INVENTION

[0004] A feature of the present invention is to provide methods for thecontrolled oxygen addition to metal particles.

[0005] An additional feature of the present invention is to provideimproved methods on the formation of metal oxides, such as metalsuboxides.

[0006] Additional features and advantages of the present invention willbe set forth in part in the description that follows, and in part willbe apparent from the description, or may be learned by practice of thepresent invention. The objectives and other advantages of the presentinvention will be realized and attained by means of the elements andcombinations particularly pointed out in the description and appendedclaims.

[0007] To achieve these and other advantages, and in accordance with thepurposes of the present invention, as embodied and broadly describedherein, the present invention relates to a method to form metal oxidematerials. One method includes forming an oxide film on a metal materialand diffusing the oxygen from the oxide film through the metal materialto form a metal oxide material.

[0008] The present invention further relates to other embodiments toform a metal oxide material. One method includes pressing the metalpowder to form a pressed article and then forming an anodic oxide filmon the pressed article. The method includes heat treating the pressedarticle to form a metal oxide material.

[0009] In another method, the metal oxide material is formed by pressingmetal powder to form a pressed article and then forming an anodic oxidefilm on the pressed article. The pressed article is then reduced to apowder or other desirable form.

[0010] The present invention further relates to products produced by oneor more of the above-identified described processes.

[0011] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory only and are intended to provide a further explanation ofthe present invention, as claimed.

[0012] The accompanying drawings, which are incorporated in andconstitute a part of this application, illustrate aspects of the presentinvention and together with the description serve to explain theprincipals of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 illustrates the capacitance change at different formationvoltages;

[0014]FIG. 2 illustrates the DCL change at different formation voltages;

[0015]FIG. 3 illustrates the cumulative pore volume versus the diameterbefore and after anode reformation;

[0016]FIG. 4 is an illustration of 10,000×SEM of an anode formed at 20V;

[0017]FIG. 5 is an illustration of 20,000×SEM of an anode formed at 20V;

[0018]FIG. 6 is an illustration of 10,000×SEM of an anode formed at 40V;

[0019]FIG. 7 is an illustration of 20,000×SEM of an anode formed at 40V;

[0020]FIG. 8 is an illustration of 10,000×SEM of an anode formed at 60V;

[0021]FIG. 9 is an illustration of 20,000×SEM of an anode formed at 60V;

[0022]FIG. 10 illustrates a linear relationship between the final oxygencontent and formation voltage; and

[0023]FIG. 11 illustrates the nitrogen and oxygen content with change offormation voltage;

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0024] The present invention relates to metal particles, and moreparticularly to metal oxide materials, such as powders, articles, andthe like. The present invention in addition relates to methods offorming metal oxide materials.

[0025] For purposes of the present invention, the metal can be any metalor alloy thereof. For instance, the metal can be any valve metal.Examples include, but are not limited to, at least one metal in Groups4, 5, and 6 (IUPAC designations) of the Periodic Table, aluminum,bismuth, antimony, and alloys thereof and combinations thereof.Preferably, the valve metal is tantalum, aluminum, titanium, zirconium,niobium, and/or alloys thereof, and most preferably is niobium,tantalum, or alloys thereof. Generally, the alloys of the valve metalwill have the valve metal as the predominant metal present in the alloy.

[0026] The metal oxide formed in the present application is a metaloxide containing one or more of the above-described metals and oxygen.

[0027] In the present invention, in one embodiment, the presentinvention relates to forming metal oxide materials, such as powders. Theprocess involves forming an oxide film on the metal material and thendiffusing oxygen from the oxide film through the metal material to forma metal oxide material.

[0028] In more detail, the oxide film formed on the metal material canbe any oxide film capable of diffusing oxygen from the film and into themetal material to form a metal oxide material. The oxide film istypically a metal oxide film and more preferably is a metal oxide filmthat contains the same metal as in the metal material. For instance,when the metal material is niobium, the oxide film is preferably aniobium oxide film, such as niobium pentoxide. Examples of othersuitable metal oxide films include, but are not limited to tantalumpentoxide, vanadium pentoxide, and aluminum pentoxide and the like.

[0029] The thickness of the oxide film is a thickness sufficient toprovide a sufficient amount of oxygen so as to at least partiallydiffuse or fully diffuse from the oxide film and into the metal materialto form the desired metal oxide material.

[0030] The diffusing of the oxide film into the metal material can beuniform or non-uniform. In other words, the diffusing of the oxide filminto the metal material can be partial or complete. If partial, thenthere can optionally be portions of the metal material that remain ametal while other portions of the metal material are converted to ametal suboxide. As an example, depending upon the thickness of the oxidefilm, a metal material can be formed wherein part of the metal materialis Nb and other parts of the metal material are converted to NbO.Preferably, the diffusing of the oxide film into the metal material isuniform to provide a substantially uniform metal suboxide material suchas, NbO. Generally, the amount of voltage applied onto the metalmaterial to form the metal oxide film will determine the amount ofoxygen present in the oxide film and thus will further determine theamount of oxygen that diffuses into the metal material to form the metalsuboxide. For instance, as shown in some of the examples, a voltage of10 volts applied to an anode type metal material will lead to a certainpercentage of oxygen formed in the oxide layer which then can bediffused into the metal material. Generally, the voltage applied to formthe oxide film will be from about 5 volts or less to about 60 volts ormore. More preferably, the voltage applied is from about 10 volts toabout 50 volts to form a satisfactory amount of oxide film to diffuseinto the metal material to form the various products of the presentinvention.

[0031] Generally, the anodization of the metal material can be achievedin any manner such as, by placing the metal material in an electrolyteand creating the desired voltage. The metal material can be in the formof a pressed and/or sintered body such as, an anode body. The pressingof the material and/or sintering of the material is optional. As long asthere is enough conductivity throughout the metal material to support acurrent density, the metal material can be in any state to achieve theformation of an oxide film. Thus, the metal powder can be placed in acontainer so that a current density is achieved throughout the metalmaterial. The metal material can be in a mold, can be pressed like ananode, and the like. Furthermore, the metal material can be processedusing water agglomeration techniques such as described in InternationalPatent Application No. WO 99/61184, incorporated in its entirety byreference herein. Depending upon the anodization voltage used, one caneasily determine the voltage achieved by the color observed afteranodization. For instance, at 10 volts, a brownish red color is seen. At20 volts, a light blue color is seen. At 30 volts, a light green coloris seen. At 40 volts, a brick red color is seen. At 50 volts, a darkbluish purple color is seen. Using the colors observed during theanodization process makes it quite easy to determine the voltageachieved as well as to determine the appropriate film thickness desiredin order to achieve the final product. For example, as a general rule,the growth rate of an oxide film on niobium metal is about 39 nm pervolt.

[0032] As indicated, the oxide film, for instance, can be an anodicoxide film, which can be formed, for instance, by applying a DC voltageto the metal material in an electrochemical cell to form the anodicoxide film. The manner in which anodization can be accomplished is asfollows. Samples can be placed in an electrolyte solution having an acidand water. Exemplary acids that can be used are H₃PO₄, H₂SO₄, etc. orcombinations of acids can be used. Additionally any type of water havingions can be used. Exemplary types of water that can be used are tapwater and/or distilled water. Preferably, the temperature of theelectrolyte solution is at 85° C.; however, the electrolyte solutionhaving other temperatures can also be used. A constant current can thenbe passed through the solution. The constant current can be any current.For example, a 135 ma/g current can be used. A preset voltage for apredetermined time can then be applied to form a desired film thickness.The product can then be soaked for a predetermined temperature and time,for example at 60° C. for 30 minutes, and then dried for a predeterminedtime and temperature. For example, the drying of the product can takeplace in an oven at about 60° C. for about 120 minutes.

[0033] In the present invention, the oxygen content eventually presentin the metal oxide material can be precisely controlled since theapplied voltage determines the thickness of the oxide film and thus theamount of oxygen diffusing ultimately into the metal material to formthe metal oxide material.

[0034] Generally, the diffusing of the oxygen from the oxide film occursto the degree that the initial oxide film dissipates into the metalmaterial. A further oxide film can also be formed. The further oxidefilm can be formed in two different manners. For example, after thefurnace treatment, as the metal/metal oxide is being cooled a pentoxidelayer can be formed on the surface. Such a formation is calledpassivation layer. Additionally, a further oxide film can be re-grown onthe surface by a second anodization process.

[0035] The metal material on which the oxide film is formed can be anyshape. The metal materials are preferably in the shape of a pressedarticle, such as a block or anode shaped material. Generally, any shapethat permits the formation of an oxide film is suitable for purposes ofthe present invention. For example, the metal material can be in a shapeof rectangle, cylinder, disk, or any other shape that allows theparticles to be in contact with each other to conduct electricity.

[0036] The preferably pressed article can be formed by any techniquesuch as taking powder and placing it in a mold and using sufficientpressure to press the metal together to obtain a pressed article. Thepressed density can be any desired density for instance, from about 1 toabout 4 g/cc. Preferably, the metal material has a high purity such as,a combined iron, nickel, chromium content of below 100 ppm and morepreferably below 50 ppm, for instance, for a valve metal such astantalum or niobium. The metal material can have essentially any Scottdensities and preferably from about 0.7 to about 5 or more g/ml. Thestarting material can be any form of metal material and in any shapesuch as, nodular, flake, platelet, and combinations thereof. Forinstance, the starting material can have BET surface areas of from about0.5 to 10 m²/g or more, and more preferably from about 2 about 3 m² /g.

[0037] Prior to diffusing the oxygen from the oxide film, any residualelectrolyte can be removed by washing or other cleaning techniques.

[0038] Once the oxide film is present on the metal material, such as thepressed article, the oxygen can be diffused from the oxide film and intothe metal material and preferably throughout the metal material topreferably form a uniform metal oxide material. The oxygen can bediffused from the oxide film using any technique. For instance, themetal material with the oxide film can be subjected to heat treating ata sufficient temperature and for a sufficient time to diffuse the oxygenfrom the oxide film through the metal material to form the desired metaloxide material. The diffusing of the oxide film into the metal materialcan be done while the metal material is in the shape of a pressedarticle or can be done after reducing the pressed article into powderform or other desirable shapes. With respect to the preferred method ofdiffusing the oxygen, the heat treatment preferably occurs at atemperature of from about 200° C. to about 1500° C., and can occur in avacuum furnace. Other temperature ranges include from about 500° C. toabout 1,200° C. for generally a time of 1 hour or so. Other sufficienttimes to achieve diffusing can be used. This allows the oxygen tohomogenize within the metal materials by way of diffusion. The heattreating at a sufficient temperature and for a sufficient time can bedone in an inert atmosphere, a hydrogen atmosphere, or in a vacuum.Generally, the temperature and the time of heat treating can be based onthe geometry of the metal material containing the oxide film. Generally,a lower temperature requires more time to achieve uniform diffusion ofthe oxygen from the oxide film while a higher temperature causesdiffusion more rapidly. Additionally, atmospheric conditions of thereactor can also influence the required time to achieve uniformdiffusion of the oxygen from the oxide film to the metal. For example,heating the metal and the metal oxide film in a hydrogen atmosphererequires less time to achieve uniform diffusion of the oxygen from theoxide film to the metal than in an argon or vacuum atmosphere.

[0039] The ultimately formed metal oxide material, as indicated above,is a metal oxide of the starting metal material.

[0040] The starting metal material can be any shape or size. Preferably,the metal material is in the form of a plurality of particles. Examplesof the type of powder that can be used include, but are not limited to,flaked, angular, nodular, and mixtures or variations thereof. Examplesof metal powders include those having mesh sizes of from about 60/100 toabout 100/325 and from about 60/100 to about 200/325 mesh. Another rangeof sizes is from about −40 mesh to about −325 mesh.

[0041] The heat treatment occurs preferably in an atmosphere whichpermits the transfer of oxygen atoms from the oxide film to the metalmaterial. The heat treatment can occur in a hydrogen containingatmosphere. In combination or alternatively, the heat treatment canoccur in an inert gas.

[0042] During the heat treatment step, a constant heat treatmenttemperature can be used during the entire heat treating process orvariations in temperature or temperature steps can be used.

[0043] In addition, the formation of the metal oxide material can beperformed in the presence of nitrogen or other doping materials in orderto prepare a metal oxide material having dopants present, such asnitrogen. The metal oxide material is any metal oxide which preferablyhas a lower oxygen content than the metal oxide film. Typical reducedvalve metal oxides comprise NbO, NbO_(0.7), NbO_(1.1), NbO₂, TaO, AIO,Ta₆O, Ta₂O, Ta₂O_(2.2), or any combination thereof with or without otheroxides present. Generally, the reduced metal oxide of the presentinvention has an atomic ratio of metal to oxygen of about 1: less than2.5, and preferably 1:2 and more preferably 1:1.1, 1:1, or 1:07. Putanother way, the reduced metal oxide preferably has the formulaM_(x)O_(y) wherein M is a valve metal, x is 2 or less, and y is lessthan 2.5x. More preferably x is I and y is less than 2, such as 1.1,1.0, 0.7, and the like. Preferably, when the reduced valve metal oxideis tantalum, the reduced metal oxide has an atomic ratio of metal tooxygen of about 1: less than 2, such as 1:0.5, 1:1, or 1:0.167 or has aratio of 2:2.2.

[0044] The present invention further relates to products prepared by oneor more of the above-described processes.

[0045] As indicated above, the metal oxide material can be then reducedinto a powder prior to or after the diffusing of the oxygen. Thereduction to particles can be done in any manner such as milling,crushing, and the like, to reduce the particles to a size of from about50 microns to about 400 microns.

[0046] The present invention in one embodiment eliminates localizedoxidation which thereby yields a homogenous product.

[0047] The present invention will be further clarified by the followingexamples, which are intended to be exemplary of the present invention.

EXAMPLES Example 1

[0048] Niobium flaked powder having a BET surface area of about 2.0 m²/gwas pressed into the shape of anodes. The pressing was achieved using aBarbuto anode press with a press density of 3.0 or 3.2 g/cc. The variousparameters of the anode fabrication are set forth below in Table 1.TABLE 1 Press Density (g/cc) 3.0 3.2 Number of Anodes Minimum of 500Minimum of 500 Powder weight (mg) 150 150 Anode length (in) 0.17850.1785 Anode width (in) 0.1785 0.1785 Anode height (in) 0.096 0.09

[0049] The anodes were sintered at a temperature of 1300° C. for 10minutes wherein the temperature of 1300° C. was achieved using a 10′/Aramp. After sintering, the anodes were anodized at 10 through 50 voltsto form a Nb₂O₅ film on the anode surfaces. The details of theanodization are set forth below in Table 2. TABLE 2 10 V Ef 20 V Ef 30 VEf 40 V Ef 50 V Ef Anodization Anodization Anodization AnodizationAnodization Number of Anodes 100 100 100 100 100 per sample per pressdensity Electrolyte 0.1% H₃PO₄ 0.1% H₃PO₄ 0.1% H₃PO₄ 0.1% H₃PO₄ 0.1%H₃PO₄ @ 85 Deg C., @ 85 Deg C., @ 85 Deg C., @ 85 Deg C., @ 85 Deg C., @4.3 mmho @ 4.3 mmho @ 4.3 mmho @ 4.3 mmho @ 4.3 mmho Constant current135 135 135 135 135 density (ma/g) Terminal Voltage 10.0 VDC +/− 0.0320.0 VDC +/− 0.03 30.0 VDC +/− 0.03 40.0 VDC +/− 0.03 50.0 VDC +/− 0.03Terminal Voltage 180 min −0/+5 min 180 min −0/+5 min 180 min −0/+5 min180 min −0/+5 min 180 min −0/+5 min Time 60 C. soak time (min)  30  30 30  30  30 60 C. oven time 120 120 120 120 120 (min)

[0050] Afterwards, the anodes were placed in a vacuum furnace whereinthe furnace was slowly evacuated to less than 20 torr. Afterwards, 50SCFH (standard cubic foot per hr.) of argon gas was introduced and thetemperature was increased to 900° F. using a ramp of 30° F. per minute.Then, the temperature was increased to 1562° F. using a ramp of 30° F.per minute. This temperature was held for 30 minutes and then thetemperature decreased. The temperature was held at 1000° F. for 5minutes and then cooled to below 200° F. where air-venting withpassivation was used. The results of the capacitance achieved for eachrespective formation voltage as well as the DC leakage for eachrespective product formed are set forth in FIGS. 1 and 2 respectively.Furthermore, the amount of oxygen in each anode was then analyzed andthe information is set forth in Table 3. The initial O content was about7811 ppm. TABLE 3 ppm O Calc. O content Voltage Total ppm O minusTheoretical (0.5 m2/g Applied (v) % O measured init. O= BET of anode) 103.54 35400 27589 26464 20 5.45 54500 46689 51573 30 6.89 68900 6108975428 40 9.06 90600 82789 82789 50 10.3 103000 95189 119732

[0051] Table 4 sets forth the various capacitance and DC leakageachieved for each product using the various formation voltages. In someanalysis conducted of the anodes, it was determined that in some samplesNb₂N was also present in the sample and this was achieved by using aniobium powder that had nitrogen levels present. Accordingly, one optionof the present invention is to start with a niobium powder having suchnitrogen levels or other dopants in order to achieve metal suboxidematerials which further contain subnitride levels or other sub-dopantlevels furthermore, based on oxygen levels, the 50 volt sample afterheat treatment was a NbO_(0.71). It was observed that the oxygen levelsincreased linearly with the formation voltage and based on thisinformation, a formation voltage of approximately 72 volts would resultin achieving a NbO product. TABLE 4 Formation Press Voltage Density 2.5Bias 10 Bias DCL DCL Oxygen (v) (g/cc) CV/g CV/g uA/g nA/CV ppm 10 3.251250 49289 55.32 1.08 38,100 20 3.2 49815 48131 70.80 1.42 58,100 303.2 48639 46536 105.27 2.16 76,200 40 3.2 47557 43411 100.73 2.12 89,70050 3.2 46956 40223 165.69 2.04 109,000

Example 2

[0052] Niobium flake powder having a BET surface area of 2.0 m²/g waspressed into the shape of anodes. The initial oxygen content of theniobium flake powder was 7811 ppm. Additionally, the niobium flakepowder also included 450 ppm of combined iron, nickel, and chromium. Thepressing was achieved using a Barbuto anode press with a press densityof 3.0 or 3.2 g/cc. The various parameters of the anode fabrication areset forth below in Table 5. TABLE 5 Press Density (g/cc) 3.0 3.2 Numberof Anodes Minimum of 500 Minimum of 500 Powder weight (grams) 150 150Anode length (cm) 0.1785 0.1785 Anode width (cm) 0.1785 0.1785 Anodeheight (cm) 0.096 0.09

[0053] The anodes were sintered at a temperature of 1300° C. for 10minutes wherein the temperature of 1300° C. was achieved by using avacuum sintering furnace (10′/A ramp). After sintering, the anodes wereanodized at 10 through 50 volts in 10 volt increments to form an anodefilm on the anode surfaces. The details of the anodzation of thisexample are identical to the details of the anodization set forth inExample 1.

[0054] Once the anodization was completed at 10 V, 20 V, 30 V, 40 V and50 V, DC to form the Nb₂O₅ film layer, leakage/capacitance-ESR testingwas performed to ensure that the Nb₂O₅ film layer was present and as abase line. The various parameters of the DC leakage/capacitance are setforth below.

[0055] DC Leakage Testing - - -

[0056] 70% Ef Anodization Voltage, 10% H₃PO₄ @ 21° C.

[0057] 60, 120, and 180 second charge time

[0058] Capacitance-DF Testing:

[0059] 18% H₂SO₄ @ 21° C., 120 Hz, Bias @ 2.5, 10 vdc

[0060] Mercury porosimetry

[0061] (a) N=3 anodes per sample for Hg submission.

[0062] Afterwards, the anodes were placed in a vacuum furnace, as inExample 1. The samples were then labeled as: (A) 10 V (B) 20 V (C) 30 V(D) 40 V (E) 50 V

[0063] The products were then anodized at 35 volts to form the metaloxide film layer. The details of the anodization are set forth below inTable 6. TABLE 6 Sample A 10 V B 20 V C 30 V D 40 V E 50 V Electrolyte0.1% H₃PO₄ 0.1% H₃PO₄ @ 0.1% H₃PO₄ 0.1% H₃PO₄ 0.1% H₃PO₄ @ 85 Deg C, 85Deg C, @ @ 85 Deg C, @ 85 Deg C, @ 85 Deg C, @ 4.3 mmho 4.3 mmho @ 4.3mmho @ 4.3 mmho @ 4.3 mmho Constant current 135 135 135 135 135 density(ma/g) Terminal Voltage 35.0 VDC +/− 0.03 35.0 VDC +/− 0.03 35.0 VDC +/−0.03 35.0 VDC +/− 0.03 35.0 VDC +/− 0.03 Terminal Voltage 180 min −0/+5min 180 min −0/+5 min 180 min −0/+5 min 180 min −0/+5 min 180 min −0/+5min Time 60° C. soak time  30  30  30  30  30 (min) 60° C. oven time 120120 120 120 120 (min)

[0064] After anodizing the product at 35 volts, DCleakage/capacitance-ESR of eight anodes per sample (A) through (E) weretested under the following conditions:

[0065] (a) DC leakage Testing - - -

[0066] 70% EF Test Voltage, 10% H₃PO₄ @21° C.

[0067] 60, 120, and 180 second charge time

[0068] (b) Capacitance-DF Testing:

[0069] 18% H₂SO₄@ 21° C., 120 Hz, Bias @ 2.5, 10 vdc

[0070] Mercury porosimetry —N=3 anodes per sample for Hg submission.

[0071] Table 7 sets forth the various capacitance and DC leakageachieved after heat cycle and reformation of the anode film layer at 35V for each product using the various formation voltages. TABLE 7 Afterheat cycle and reformation at 35 V DCL Formation 2.5 V Bias 10 V BiasuA/g @ Oxygen Lot Trial Voltage CV/g CV/g 60 s (ppm) Flake 1 10 5125049289 55.32 38100 Flake 1 20 49815 48131 70.8 58100 Flake 1 30 4863946536 105.27 76200 Flake 1 40 47557 43411 100.73 89700 Flake 1 50 4695640223 95.8 109000

[0072] The pore structure of the sintered and formed anodes was measuredafter the first and second anodization step. The total pore volumeincreased after the second anodization when compared to the firstanodization. There was also more volume present and larger porediameters after the second formation. This indicates that the anodeswill be easier to impregnate with MnO₂ after the second formation thanafter only the first formation. The anodes formed at the lowest initialvoltages had the highest total pore volume. This is due to the growth ofthe Nb₂O₅ film, which is proportional to the formation voltage. At lowervoltages, the Nb₂O₅ film grows the least and consumes the smallestamount of the pore volume. FIG. 3 illustrates the cumulative pore volumeversus the diameter for the anode before and after anode reformation.

[0073] Example 3

[0074] Niobium flake powder having a BET surface area of about 2.0 m²/gand having an initial oxygen content of 7811 ppm and 450 ppm of combinediron, nickel, and chromium was pressed into the shape of anodes.Additionally, nodular niobium having a BET surface area of 2.0 m²/g andhaving an initial oxygen of 8000 ppm and 23 ppm of combined iron,nickel, and chromium was pressed into the shape of anodes. The pressingwas achieved using a Barbuto anode press as in Example 2. The anodeswere also sintered in accordance to the sintering process of Example 2.After sintering, the anodes were anodized at 20, 40, 50, 60 and 70volts. Except for the formation voltages, the details of the anodizationwere identical to the anodization procedure of Example 2. Similarly, theDC leakage/capacitance testing was identical to the DCleakage/capacitance testing of Example 2. Additionally, the furnaceprocedure, the anode reformation, and testing were identical to thefurnace procedure and the anode reformation and testing of Example 2.

[0075] Table 8 sets forth the various capacitance and DC leakageachieved after heat cycle and reformation at 35 V to reform the metaloxide film layer for each product using the various formation voltages.TABLE 8 After heat cycle and reformation mat 35 V 2.5 V 10 V DCLFormation Bias Bias uA/g @ Lot Trial Voltage CV/g CV/g 60 s Oxygen (ppm)Flake 2 20 54899 52921 79.52 61800 Flake 2 40 54833 50084 138.55 98200Flake 2 50 55156 47363 150.95 113000 Flake 2 60 55038 44928 177.68142000 Flake 2 70 59651 46404 342.26 181000 Nodular 2 20 57527 5141047.67 53700 Nodular 2 40 60998 49022 39.2 87800 Nodular 2 50 63792 4782331.31 98700 Nodular 2 60 63891 46112 27.63 124000 Nodular 2 70 6372946071 25.8 154000

[0076]FIGS. 4-9 illustrate anodes made from niobium flake that wereanodized at 20, 40, or 60 V. FIG. 4 is an illustration of 10,000×SEM ofan anode formed at 20 V. FIG. 5 is an illustration of 20,000×SEM of ananode formed at 20 V. FIG. 6 is an illustration of 10,000×SEM of ananode formed at 40 V. FIG. 7 is an illustration of 20,000×SEM of ananode formed at 40 V. FIG. 8 is an illustration of 10,000×SEM of ananode formed at 60 V. Finally, FIG. 9 is an illustration of 20,000×SEMof an anode formed at 60 V.

[0077] The linear relationship between the final oxygen content andformation voltage of Examples 2 and this example can be seen in FIG. 10.R2 values indicate a good correlation between voltage and oxygen for theflake samples (R2=0.96) and for all samples (R2=0.94) in general.

Example 4

[0078] Two sets of samples were prepared. The first set of samples wasprepared by pressing 4 wafers of niobium flake having a BET surface areaof about 4 m²/g into a pellet of approximately 0.75″ diameter and 0.1″high using an isostatic press. The pellets were then placed in 1% H₃PO₄solution and formed at 0, 20, 40, or 60 volts until current decays tobelow 0.1 amps, which indicated that the film is no longer growing. Thepellets were then labeled and were placed in a furnace similar to theone in Example 1. Samples were then tested for oxygen after the furnacetreatment.

[0079] In the second set of samples, the same type of niobium powder wasplaced in a ceramic crucible with water and mixed to water agglomerate.The crucibles were then placed in a HT-3 Solar Atmospheres Furnace, Inc.wherein the furnace was slowly evacuated to less than 20 torr. Thefurnace was then back filled with argon and then slowly evacuated againto a rough vacuum. Argon was then introduced and continued throughoutthe run. The temperature was increased to 2192° F. The temperature washeld for 30 minutes and then the temperature was decreased to 1000° F.using a ramp of 30° F. per minute. The temperature was held at 1000° F.The furnace was then cooled with argon flowing until the temperaturereached below 150° F. The argon gas was then stopped and the furnace wasevacuated to 20 torr. Air was introduced in 100 torr intervals untilatmospheric pressure was obtained. The samples were then removed fromthe furnace and allowed to cool.

[0080] The crucible was then anodized in a similar manner as the niobiumflake in the previous sample by placing the crucible in a H₃PO₄ solutionand anodized at 20 or 30 volts. After the anodization process, thesample sets were placed in a furnace identical to the furnace used inExample 1. Samples were then tested for oxygen content after the furnacetreatment.

[0081] The heat treated/H₂O agglomerated materials picked up a largeamount of oxygen and nitrogen during the anodization and subsequent heattreatment at 1562° F. in argon. These samples were labeled as “powder”in the FIG. 11 and Table 9. The pressed disks anodized at 0, 20V, 40V,and 60V also picked up a significant amount of oxygen during the heattreat and anodization steps. TABLE 9 Voltage O (ppm) N (ppm) Disk 022468 181 Disk 20 53361 300 Disk 40 53627 247 Disk 60 86847 316 Powder 015743 128 Powder 20 25230 2205 Powder 30 54988 7144

[0082] Other embodiments of the present invention will be apparent tothose skilled in the art from consideration of the present specificationand practice of the present invention disclosed herein. It is intendedthat the present specification and examples be considered as exemplaryonly with a true scope and spirit of the invention being indicated bythe following claims and equivalents thereof.

What is claimed is:
 1. A method to form a metal oxide materialcomprising diffusing oxygen from an oxide film present on the metalmaterial to form a metal oxide material.
 2. A method to form a metaloxide material comprising forming an oxide film on a metal material; anddiffusing oxygen from said oxide film through said metal material toform a metal oxide material.
 3. The method of claim 2, wherein saidmetal material is a metal powder which is formed into a pressed article.4. The method of claim 2, wherein an anodic oxide film is formed on themetal material to form said oxide film.
 5. The method of claim 2,wherein said diffusing is achieved by heat treating said metal material.6. The method of claim 5, wherein said metal material is reduced to apowder prior to heat treating.
 7. The method of claim 2, wherein saidmetal material is niobium.
 8. The method of claim 2, wherein said metalmaterial is a valve metal.
 9. The method of claim 2, wherein said oxidefilm is niobium pentoxide.
 10. The method of claim 2, wherein saiddiffusing of said oxygen is uniform throughout said metal material. 11.The method of claim 2, wherein said diffusing is partial wherein a metaloxide material is formed and is present with a portion of said metalmaterial.
 12. The method of claim 2, wherein said oxygen diffusesthrough a portion of said metal material to form a metal oxide materialand a core of metal material is not converted to a metal oxide material.13. The method of claim 4, wherein said anodic oxide film is formed byapplying a voltage of from about 10 volts to about 100 volts to saidmetal material to form said anodic oxide film.
 14. The method of claim13, wherein said voltage is from about 10 to about 80 volts.
 15. Themethod of claim 5, wherein said heat treating is at a temperature of atleast 200° C. for a sufficient time to diffuse said oxygen from saidoxide film to at least a portion of said metal material.
 16. The methodof claim 15, wherein said heat treating is at a temperature of fromabout 200 to about 1500° C.
 17. The method of claim 2, furthercomprising reanodizing said metal oxide material to form an oxide filmon said metal oxide material.
 18. The method of claim 2, wherein saidmetal material is niobium and said oxide film is niobium pentoxide. 19.The method of claim 2, wherein said metal oxide material is NbO.
 20. Themethod of claim 2, wherein said metal oxide material has an atomic ratioof niobium to oxygen of less than 2:1.
 21. The method of claim 20,further comprising reanodizing said metal oxide material to form anoxide film on said metal oxide material.
 22. The method of claim 18,wherein said metal oxide material is NbO.
 23. The method of claim 18,wherein said metal oxide material has an atomic ratio of niobium tooxygen of less than 2:1.
 24. A metal oxide material formed by the methodof claim
 1. 25. A metal oxide material formed by the method of claim 2.26. A metal oxide material formed by the method of claim
 3. 27. A metaloxide material formed by the method of claim
 17. 28. A metal oxidematerial formed by the method of claim
 18. 29. A metal oxide materialformed by the method of claim
 19. 30. A metal oxide material formed bythe method of claim
 20. 31. A metal oxide material formed by the methodof claim
 21. 32. A metal oxide material formed by the method of claim22.